1. Field of the Invention
This invention relates to processes for increasing the relative viscosity (RV) of a reactant polyamide through the use of chain extender compounds and to polyamide products incorporating chain extender moieties in their polyamide chains.
2. Description of Related Art
Various methods have been proposed to impart high viscosity to polyamides.
Catalysts are employed to speed up the reaction. For example, polyamide 6,6 synthesis involves the reaction of a diamine (hexamethylene diamine) and a diacid (adipic acid) to produce the polyamide 6,6 and water. The rate of formation of the polyamide depends greatly on the removal of water from the reaction system. Catalysts do speed up the reaction but water removal remains the rate determining factor.
Another method to impart a high viscosity to polyamides is referred to as chain extension. Chain extension is based on a reaction between a polyamide chain end group (an acid end group or an amine end group) and a chain extender molecule with two reactive end groups that react with either the amine end group or the acid end group of the polyamide to connect two polyamide chains. Prior use of chain extenders with polyamides did not increase RV enough to adopt the technology. The use of bis-lactams for polyamidation acceleration was disclosed by Flory in U.S. Pat. No. 2,682,526.
There is a need to take low RV polyamide and rapidly increase its RV to a predictable final product with a higher RV.
These and other objects of the invention will be clear from the following description.
The invention relates to a process for increasing the relative viscosity (RV) of a reactant polyamide, including:
contacting the reactant polyamide and a chain extender compound selected from the group consisting of bis-N-acyl bislactam compounds and mixtures thereof, both in a liquid phase, the reactant polyamide having a starting RV, a concentration of amine end groups (AEG(R)), and a concentration of carboxyl end groups (CEG(R)) with the AEG(R) being greater than the CEG(R), the chain extender compound having a concentration of lactam end groups (LEG) of at least about 10 equivalents per million grams of the reactant polyamide less than the AEG(R), for a duration of about 0.5 minutes to about 10 minutes, increasing the RV of the reactant polyamide;
forming a product, other than flake; and
quenching the product to room temperature such that the product has a final RV greater than the starting RV and a concentration of amine end groups (AEG(P)) as defined by the formula:
AEG(P)={AEG(R)xe2x88x92LEG}xc2x1Xxe2x80x83xe2x80x83(1) 
wherein:
AEG(P) is the concentration of amine end groups in the quenched product in units of equivalents/1,000,000 gms of the product;
AEG(R) is the concentration of amine end groups in the reactant polyamide in units of equivalents/1,000,000 gms of the reactant polyamide;
LEG is the concentration of lactam end groups in the chain extender compound in units of equivalents/1,000,000 gms of the reactant polyamide; and
X is any number in a range of about 0 to about 5.
The invention is further directed to a product made by the process of the present invention. A preferred product is a filament, comprising:
a synthetic melt spun polymer including:
polyamide repeating units (R1);
polyamide chain extender moieties (R2), each independently, selected from the group consisting of bis-N-acyl bislactam moieties; and
terminal groups (R3), each independently, selected from the group consisting of a hydrogen atom and a hydroxyl group;
the polymer including chains, each independently, having a chemical structure:
R3xe2x80x94(R1xe2x80x94R2)yxe2x80x94R1xe2x80x94R3xe2x80x83xe2x80x83(2) 
wherein y is an integer of 1-7; and
the filament has a formic acid relative viscosity of at least about 30.